1. Technical Field
The present invention relates to a multi-gap type electric rotating machine which is used in, for example, a motor or a generator for a vehicle.
2. Related Art
As a conventional art, JP-A-2007-282331 discloses a double stator type motor. This double stator type motor has an annular rotor connected to a rotating shaft via a rotor disc, an inner stator disposed inside the rotor in the radial direction thereof, and an outer stator disposed outside the rotor in the radial direction thereof. In addition, double gaps are provided between the rotor and both the inner and outer stators and in the radial direction of the rotor. Thereby, higher torque can be generated compared with a single stator type motor.
To further increase the output of the motor, multiple gaps can be considered as the simplest way. That is, in addition to the gaps provided between the rotor and both the inner and outer stators and in the radial direction of the rotor, a side stator may be disposed at one end side of the rotor in the axial direction thereof to provide a gap in the axial direction. This is a way of providing three gaps.
However, the above-described multi-gap structure has not been in practical use. The main reason is that if an iron core of the side stator is formed of usual laminated steel sheets, eddy currents are generated in the lamination planes due to magnetic flux flowing in the laminated direction, which increases losses and significantly decreases the output of the motor.
In addition, as a method of decreasing losses, a so-called powder magnetic core, which is formed by pressurizing soft magnetic powder to which insulating coating is applied, may be used as material of the iron core of the side stator. However, the powder magnetic core has many problems in practice such as a decrease in output due to the magnetic properties thereof being lower than those of a magnetic steel sheet, an increase in manufacturing costs, and mechanical weakness which leads unreliability.